European patent number EP1,549,459 teaches a method and device for determining a positioning error of a CNC machine tool head or machine table. According to the method, a support base is equipped with a plurality of distance sensors to determine the Cartesian coordinates of a gauge tool equipped with a ball. In order to determine the positioning error of the tool head, the plurality of distance sensors measure the respective distances to the ball. Then the tool head or table performs an angular motion whereas at the same time the machine performs a circular or helical counter motion such that the ball of the gauge tool remains in its position. Then the plurality of distance sensors measure the respective distances to the ball again. Due to a positioning error of the tool head these distances may differ. Then the machine is caused to perform a linear motion with respect to the Cartesian coordinate axes so that the plurality of distance sensors measure the original distances again, whereas at the same time the angular position of the head or table remains fixed. From this compensation movement, the positioning error of the head or table may be determined as the linear motions which were necessary to compensate the positioning error of the head or table.
The device of EP1,549,459 has a controls for the CNC machine that reads and processes the data from the plurality of sensors. When there is no common interface between the plurality of sensors and the CNC machine available, e.g. because both devices were fabricated by different manufacturers, the controls has to be configured to interface to sensors with different types of interfaces.
There is a need for a method and device for determining a positioning error of a CNC machine, in particular, of a CNC machine tool head and/or a CNC machine table, which works independently of the control of the CNC machine and, in particular, requires no common interface with the control of the CNC machine.